334 



MANUAL OF ZOOLOGY. 



unite and become specially modified to form the thorax, to 

 which the three pairs of locomotive limbs, characteristic of per- 

 fect Insects, are attached. Two additional pairs of locomotive 



Fig- 175- A, One of the Dragon-flies (sEskna grandis), slightly dissected : h Head, 

 carrying the eyes, antennae, and organs of the mouth ; t t' t" First, second, and third 

 segments of the thorax slightly separated from one another, each carrying a pair of 

 legs, and the two last carrying each a pair of wings ; a Tail or abdomen. B, Young 

 form, or "larva," of the same. C, Second stage, or " pupa." D, Head of a Dragon- 

 fly (Libellula depressa), showing the feelers or antennae (0.11), the eyes (e e), the hinder 

 pair of jaws (;), and the upper lip (f). 



organs, the wings, are developed, in most insects, from the 

 tergal walls of the second and third thoracic somites. No 

 locomotive limbs are ever developed from the abdomen of the 

 adult insect ; but the ventral portions of the abdominal somites, 

 from the eighth backwards, are often metamorphosed into ap- 

 paratuses ancillary to the generative function " (Huxley). 



The integument of the Insecta, in the mature condition, is 

 more or less hardened by the deposition of chitine, and usu- 

 ally forms a resisting exoskeleton, to which the muscles are at- 

 tached. The segments of the head are amalgamated into a 

 single piece, which bears a pair of jointed feelers or antennae, 



